There's another kind of hard firebrick, called "high alumina", which is used in soda and salt wood-firing pottery. The alumina content resists the sodium oxide from the salt or soda decomposing in the wood fire.

It's on my todo list one day to build a wood fire kiln out of "splits" of high alumina on the inside and 2800 rated IFB on the outside, to do my own soda firing. IFB absorbs water so it has to be protected from the elements with a roof and walls, but it's worth it given how much efficiency you gain.

There's an interesting playlist of videos about wood fired kilns for pottery here:

https://www.youtube.com/watch?v=2_wVFkKwCmg&list=PLS6Mrdpt53...